The invention relates to a device for sensing a displacement or to a linear displacement sensor for a linear drive displacing an actuator such as an actuator rod substantially linearly, mainly in its axial direction. Linear drives are used particularly for controlling a positioner such as a turbocharger, a turbobrake, a valve or the like.
Such devices or displacement sensors are known to be integrated particularly in pneumatic linear drives such as aneroid capsules or pressure cans. Known from published German patent application DE 43 03 403 A1 is a pneumatic linear drive, the pneumatic working chamber of which is defined in part by a diaphragm stiffened by a disc. When the working chamber is exposed to a vacuum, the volume of the working chamber is reduced and the diaphragm, together with the stiffening disc, is displaced. The actuator secured to the stiffening disc exerts a corresponding actuation response for controlling the positioner. A bar magnet accommodated in the actuator is displaced relative to a fixed magnet sensor during positioning. The magnet sensor senses the position of the actuator from the change in the magnetic field and relays a displacement signal to a corresponding controller. A similar configuration of a linear displacement sensor is known from German patent application DE 196 24 233 C1.
In many positioners, such as turbochargers or turbobrakes, operating forces occur having radial direction components as regards the axial direction of displacement of the actuator. These radial force components are evident by a drift in the parts of the positioner from their displacement path and are transferred to the actuator of the linear drive which consequently results in a departure of the actuator from its linear displacement path. Known displacement sensor systems have problems in that they either prove unsuitable for such positioners as turbochargers because of the actuator guidance being too rigid or the results of sensed displacement of the actuator differ markedly from the true displacement because of strong radial force components of the positioner. This distortion in the displacement sensings can greatly detriment positional control.